1. Field of the Invention
The present invention relates to a housing structure and a housing process for a display device and, more particularly, to a housing structure with multiple sealing layers for an organic EL element device.
2. Description of the Related Art
In an electro-luminescence (EL) element used for a display device, electric current applied to specific fluorescence or phosphorus can transform electricity into luminosity. According to the different materials used in the luminescent layer, EL elements are classified as organic and inorganic, wherein the organic EL element device employs laminated organic layers and has the advantages of thin profile, light weight, high luminescent efficiency, and low driving voltage. However, since the active lifetime and reliability is highly concerned with the housing structure, it is importance to develop an improved housing process for the organic EL element device.
Presently, the organic EL element uses active metal of low work function to form a metallic cathode, thus the active lifetime of the organic EL element is highly concerned with moisture and oxygen present in the organic EL element. As the duration of use increases, the likelihood of moisture and oxygen permeating the organic EL element also increases, causing detachment between the organic luminescent layer and the cathode, cracking of the organic materials, and oxidation of the electrodes. As a result, a so-called xe2x80x98dark spotxe2x80x99, to which electricity is not supplied, is generated, decreasing luminescence and luminescent uniformity. In order to prolong the active lifetime, various technologies of reducing the interior humidity, to solve the problem of the dark spot, have been developed, such as forming photo-hardened resin on the glass substrate, plating metal oxide, fluoride or sulfide on the glass substrate, forming a water-resistant film on the glass substrate, and using an airtight case to package the organic EL element. Nevertheless, other problems, such as leakage current, crosstalk and oxide dissolution, remain to be solved.
FIG. 1 is a sectional diagram showing a first housing structure for an organic EL element 10 according to the prior art. An organic EL element 10 comprises a glass substrate 12, a lamination body 14 formed by an anode layer 11, an organic luminescent material layer 13 and a cathode layer 15, and a sealing agent 16 covering the lamination body 14. In housing process, a sealing cap 18 is fixed over the glass substrate 12, and then the sealing cap 18 is pressed on the sealing agent 16 by a uniform pressure and the sealing agent 16 is cured by heating. However, the thermal curing must proceed in a specific atmosphere in which moisture and oxygen are severely controlled and requires a long heating time, therefore this housing process cannot satisfy the demands of mass production.
FIG. 2 is a sectional diagram showing a second housing structure for an organic EL element 20 according to the prior art. The second housing structure provides a sealing agent 24 on the rim of the glass substrate 12 to bond the sealing cap 18 and the glass substrate 12, resulting in an airtight space 22. The sealing agent 24 is UV-cured resin that can be cured by UV irradiation to reduce the housing process time. Nevertheless, the UV-cured resin is epoxy resin containing a large amount of moisture and presenting outgassing, therefore the single-layered sealing agent 24 cannot provide good water/oxygen-resistance for the organic EL element 20.
FIG. 3A is a top view showing a metallic cap of a third housing structure for an organic EL element 30 according to the prior art, and FIG. 3B is a sectional diagram showing a third housing structure for an organic EL element 30 according to the prior art. The third housing structure provides a stamping-form metallic cap 32 which has a concavity facing the lamination body 14, a water-absorbentable layer 34 disposed in the cavity and an unidirectional penetrating film 36 covering the water-absorbentable layer 34. Preferably, the water-absorbentable layer 34 is of solid-state compounds, such as BaO, CaO, CaSO4 and CaCl2 for absorbing moisture and maintaining a solid state. Also, the moisture absorbed by the layer 34 can stay in the cavity without flowing from the unidirectional penetrating film 36. This housing structure could pass the strict circumstance test, but the metallic cap 32 without a planar surface decreases the efficacy of water/oxygen-resistance ability, and causes difficulties in manufacturing a larger-size organic EL element device. In addition, since the thickness of the metallic cap 32 is greater than that of the glass substrate 12, the organic EL device element 30 cannot achieve the aims of light weight, thin thickness, short measure and small size for planar display market.
The present invention provides a housing structure and a housing process to solve the problems found in the prior art. A transparent substrate is provided with a completed luminescent device. The rim of the transparent substrate is bonded to the rim of a sealing cap to form an airtight space. A sealing structure with a first sealing layer and a second sealing layer is provided on the bonding rim between the sealing cap and the transparent substrate. The materials used to form the first sealing layer and the second sealing layer are different.
Accordingly, it is a principal object of the invention to provide a housing structure to prolong active lifetime of display device.
It is another object of the invention to provide a housing structure to improve resistance to moisture and oxygen.
Yet another object of the invention is to provide a housing structure to improve adhesion.